This invention relates generally to electric circuit breakers with elecrical sensing units of the electromagnetic type in which the electrical sensing unit is in a circuit separate from the electrical circuit of the circuit breaker contacts. Such circuit breakerss are commonly known as "relay type circuit breakers". More particularly, this invention relates to relay type circuit breakers having linkage mechanisms with contacts which are not engageable when the electrical sensing units thereof are energized above predetermined levels, even though the linkage mechanisms are moved to the contacts closed positions. This type of linkage mechanism is generally known in the art as a "trip free" linkage mechanism and the circuit breaker is known as a "trip free circuit breaker".
Many circuit breakers are known and shown in the prior art having trip free mechanisms. For example, U.S. Pat. Nos. 3,329,913 and 3,273,089 (both assigned to the Heinemann Electric Company) illustrate circuit breakers with such mechanisms.
Electromagnetic circuit breakers with such trip free mechanisms typically comprise a movable contact, mounted on a movable arm, and a stationary contact. The circuit breaker also includes a linkage mechanism having an operating handle and a movable arm on which the movable contact is mounted. The linkage mechanism further includes a collapsible toggle assembly, the latter including a locking or latching device. The movable and stationary contacts are opened or closed by pivoting back and forth the operating handle which then moves the movable contact toward engagement or away from engagement with the stationary contact.
The electromagnetic device includes a coil and an armature which (upon predetermined energization of the coil) moves to an actuated position. The armature includes a portion which in the actuated position engages and rotates the locking device, unlatching the latter, whereupon the toggle assembly collapses and the contacts open.
As long as the coil is energized above the predetermined level, the armature remains in its actuated position, and any attempt to reclose the contacts will move the locking device into engagement with the armature, causing the toggle assembly to again collapse, whereupon it is usually not possible to complete the movement of the movable arm toward the contacts closed position. Instead, the movable arm moves to the contacts open position under the bias of a spring which tends to bias the movable arm to its contacts open position.
While the foregoing is the "usual" sequence in the prior art devices, it has been found that because of the inertia of the movable arm and the associated collapsible toggle assembly, if a sufficient force is applied to the operator, the movable arm sometimes attains sufficient momentum to continue its travel toward the stationary contact, even after the locking device has been unlatched by the armature, causing the movable and stationary contacts to momentarily touch each other and thereafter to separate. This momentary reclosing of the contacts may be undesirable and may even damage the load connected to the circuit breaker.